1. Field of the Invention
The present invention relates to a device for bus coupling between enclosed switchboards with an insulating gas sealed therein, such as cubicle type gas-insulated switchgear.
2. Description of the Related Art
FIG. 3 shows a schematic construction of a known conventional cubicle type gas-insulated switchgear 100 employing a square container. The switchgear 100 includes a plurality of cubicles 101, 102, 103, and 104. The cubicles 101, 102, 103, and 104 accommodate devices for each unit circuit, such as a circuit breaker, a disconnector, and a transformer for measuring instruments. Power is supplied to the switchgear 100 through a power receiving cable 105. The cubicles 101, 102, 103, and 104 are electrically connected via T-shaped bushings 31 by insulated coupling buses 35 for establishing communication between switchboards.
FIG. 4 shows an example of a specific structure of the conventional known T-shaped bushing 31 used in the gas-insulated switchgear 100. The T-shaped bushing 31 is disclosed, for example, in FIG. 8 of Japanese Laid-open Patent Application No. 60-160309.
As shown in FIG. 4, the conventional T-shaped bushing 31 includes a T-shaped bushing mold 41 with a substantially T-shaped current-carrying conductor 32 integrally formed therein. The T-shaped bushing mold 41 is normally molded using an epoxy resin. The current-carrying conductor 32 is formed to have a substantially T shape by a cylindrical shielding electrode 32a and a conductor drawing-out rod 32b that juts out perpendicularly in a radial direction from a central outer periphery of the shielding electrode 32a. A contact 39 is disposed on an inner periphery of the shielding electrode 32a. The contact 39 is formed such as by inserting an elastic conductive plate, which has many punched holes, along an inner periphery of a concave groove 42 provided in an inner periphery of the shielding electrode 32a. 
To connect the cubicles 101, 102, 103, and 104 by the T-shaped bushings 31 constructed as set forth above, the coupling buses 35 formed of a bridging polyethylene insulated cable that has been cut to a predetermined length are used.
First, both ends of the coupling bus 35 are stripped to expose a conductor 43 and an insulator 44 (only one end is shown in FIG. 4). Then, a stress cone 46 for relieving the electric field of a shielding layer 45, a pressing member 47 such as a spring that presses the stress cone 46 toward a connection port 40 of the coupling bus 35, a protective tube 48 for protecting the end of the coupling bus 35, etc. are attached to an outer periphery of the exposed insulator 44.
Subsequently, a conductive plug 49 which has an outside diameter substantially equal to or greater than an outside diameter D of the coupling bus before the coupling bus 35 is stripped and which is to be closely fitted to the contact 39 is attached to the end of the conductor 43. The plug 49 is disposed such that it is closely fitted to the contact 39, and the required components, including the stress cone 46, that have been attached in advance, are disposed at predetermined positions, and these components are then assembled by common means. In FIG. 4, reference numeral 104 denotes a cubicle, which is identical to the one shown in FIG. 3, reference numeral 50 denotes a blank cap, reference numeral 51 denotes a seal, reference numeral 52 denotes an external semiconductive layer, and reference numeral 53 denotes a shield.
However, since the conventional device for bus coupling between the enclosed switchboards with an insulating gas sealed therein uses the bridging polyethylene insulated cable cut to a predetermined length as the coupling bus 35, the stripping process is cumbersome and it is also difficult to improve machining accuracy. Furthermore, as the ends of the coupling bus 35 are stripped, the seal 51, the protective tube 48, the stress cone 46, etc. are required. This results in a complicated structure, a cumbersome assembly process, a prolonged assembly time, and an increased cost.
Accordingly, the present invention has been made with a view toward solving the problems with the prior art, and it is an object of the invention to provide an inexpensive device for bus coupling between enclosed switchboards with an insulating gas sealed therein that has a simpler structure and permits a shortened time for assembly.
To this end, according to one aspect of the present invention, there is provided a device for bus coupling between enclosed switchboards with an insulating gas sealed therein, comprising: a coupling bus for establishing communication between switchboards that have an insulating gas sealed therein and which accommodate electric units; a T-shaped bushing that has a current-carrying conductor integrally molded therein, a connection port for the coupling bus, and a contact for making connection between the coupling bus and the current-carrying conductor; and a fixture for securing an end of the coupling bus that has been inserted in the connection port of the T-shaped bushing, wherein a bore shape of the connection port for the coupling bus in the T-shaped bushing is a conical shape in which the diameter thereof increases outwardly, the coupling bus has a central conductor composed of a one-wire conductor, an insulating rubber member covering an outer peripheral surface of the central conductor, and a conductive layer formed on the outer peripheral surface of the insulating rubber member, in which both end portions of the insulating rubber member are formed into conical portions that fit to the connection port, a portion between both end portions is formed into a cylindrical portion having a uniform diameter, and a boundary portion between the cylindrical portion and the conical portions is formed into a stepped portion so that the outside diameter of the cylindrical portion is smaller than the outside diameters of the conical portions, the fixture secures the coupling bus by pressing the stepped portion into the connection port, and the conductive layer is provided only on an outer peripheral surface of the cylindrical portion, and further, is grounded.
The coupling bus according to the present invention may have a conductive layer between an inner surface of the insulating rubber member and the outer peripheral surface of the central conductor.
The device for bus coupling between enclosed switchboards with an insulating gas sealed therein according to the present invention may be provided with an air unit coupling bushing at one of the connection ports of the T-shaped bushing. In this case, the air unit coupling bushing is equipped with a central conductor and an insulating rubber member covering the central conductor. One end of the insulating rubber member is formed into a conical portion that fits to the connection port, and an outer peripheral surface on an outer side of the connection port in the insulating rubber member is provided with ribs that have an outside diameter larger than the outside diameter of the conical portion.